Add itersubjects to Storage class #60
Description
It's pretty common to iterate over subjects in post-experiment analysis and that's kind of clunky at the moment:
storage = Storage('data')
for subj in storage.subject_ids:
storage.subject_id = subj
reader = storage.require_task('sometask')
...Better:
storage = Storage('data')
for subj in storage.itersubjects():
reader = storage.require_task('sometask')
...It'd also be pretty rad if you could optionally pass a task to get the reader object instead:
storage = Storage('data')
for reader in storage.itersubjects(task='sometask'):
...Should be pretty straightforward to implement.